In a burst transmission, a short preamble is attached and transmitted at a beginning of burst transmission, and a receiving unit performs a timing synchronization, frequency synchronization, phase synchronization, and the like for each burst using the short preamble to detect a signal.
However, synchronization may not be accurately performed in a poor communication environment such as an environment with a low signal to noise ratio (SNR), although it depends on a synchronization method. Accordingly, a residual frequency/phase error significantly remains.
Due to the residual frequency/phase error, a signal outside of a signal mapping grid section where a signal is to be mapped may occur, and thus an error rate when detecting a signal based on a hard decision may increase.
Also, instead of an error correction method in a conventional art, a method of estimating a frequency/phase error using open symbols, inserted in a burst symbol row, is used to precisely estimate a frequency/phase error in a data area. The error correction method in the conventional art inserts an open symbol in only a beginning of a burst, obtains an estimation value of a frequency/phase error, and corrects a frequency/phase error of remaining data of the burst using the estimation value.
In this case, a frequency/phase error estimation with respect to an open symbol of an end of a burst is required to stand by for frequency/phase error estimation with respect to a beginning of burst. Accordingly, a storage device to store all symbols is required, detection may be delayed until an end of burst is processed, and transmission efficiency may decrease.
To overcome the above-described disadvantages, a technology which removes a phase error in a data symbol by estimating a phase using a pilot symbol and demodulated symbol, that is, a technology which feedbacks a symbol demodulation result in a symbol unit for a phase error calculation, has been provided. However, in the technology described above, a low SNR may cause error propagation, and thus performance may be significantly deteriorated.
Thus, a recursive demodulation apparatus and method which efficiently removes a residual frequency/phase error through a recursive demodulation in a predetermined signal block (segment) with respect to a data section of burst signal is required.